PB2165: THE CO-REBREATHING METHOD IS A RELIABLE TEST IN DETERMINING THE RED CELL MASS: THE OLD POTS MAKE THE BEST SOUPS.
Authors: Nada Maaziz, Marjolaine Georges, Damien Basille, Matthieu Gallet, Betty Gardie, Loic Garçon, François Girodon
Journal: HemaSphere (2023)

Topic: 15. Myeloproliferative neoplasms - Biology & Translational Research Background: The definition of polycythemia, whether primary or secondary, is based on direct measurement of red cell mass (RCM) by isotope labelling method. Because of the lack of availability of isotopes, the use of hematocrit and hemoglobin values defined by the WHO recommendations has overtaken the use of the RCM, which can result in misdiagnosis of polycythemia. This determination is also useful for patients with myeloproliferative neoplasm (MPN) to separate two clinical entities: essential thrombocythemia and “masked” Polycythemia Vera, both of which result in high blood counts. These two conditions have different prognoses and therapeutic management. RCM measurement is also sometimes used in the follow-up of MPN with splanchnic thrombosis. The CO-rebreathing method is mainly used in sports to assess the RCM. It is minimally invasive, fast (<30 min) and its accuracy appears to be equivalent to the gold standard’s. To date, no study has compared RCM values obtained with CO-Rebreathing and with the state-of-the-art technique, i.e. isotopic labeling, in the diagnosis of polycythemia. Aims: Here, we present the result of a prospective bi-centric study comparing RCM obtained by CO-rebreathing and by isotopic measurement in a population referred to hematologists for suspicion of polycythemia. Methods: Forty-two patients were initially recruited for simultaneous RCM determination by Co-rebreathing and isotope labelling method. All patients signed an informed consent form. During the course of the study, two patients could not benefit from the Co-rebreathing measurement due to non-compliance with the inclusion criteria (smoking just before the examination) or due to the ergonomic complexity of using the spirometer. On the other hand, the isotope labelling method could not be performed for another patient. This prospective non-randomized study therefore included 39 patients (35 men and 4 women) with a median age of 57 years (range 19-91 years); three of them had Polycythemia Vera with a V617F JAK2 mutation. The isotope labelling method was performed according to the recommendations of the French Society of Radiopharmacy (SoFRa) in a nuclear medicine department using the labelling of the patient’s red blood cells (RBC) with technetium 99m. Co-rebreathing measurement was performed in a pneumology department immediately after the respiratory functional explorations and the determination of baseline HbCO. This method consists of labelling Hb with inspired carbon monoxide (CO), resulting in a temporary increase of COHb. Results: True polycythemia was defined by an increased red cell mass (RCM) above 125% of the theoretical one, for both techniques. All results were expressed as a percentage of the theoretical value. Comparing the RCM results obtained with these two methods, the two techniques were consistent for 31 patients (21 true polycythemia, 10 false polycythemia). For four patients, the CO-rebreathing measurement was underestimated, while for four others, the value obtained by CO-rebreathing was overestimated. Overall, the method yielded a sensitivity of 84% and a specificity of 71%. Summary/Conclusion: This study, carried out on a large series of patients, allows the validation of a simple, non-invasive and reliable tool for the measurement of RCM based on the use of CO-rebreathing, and which is well correlated with the reference isotopic method. It has the advantage of being more accessible to patients, for whom a hospital hosting a nuclear medicine department is too far. In addition, it will allow the measurement of RCM in countries where the isotopic method is no longer available, such as most European and North American countries. Keywords: Erythrocytosis, Diagnosis